Section A (15 marks) Answer all questions in this section 1. Which of the following equations corresponds to the definition of standard enthalpy change of formation of carbon monoxide? A. C(g) + O(g) CO(g) B. C(g) +½ O(g) CO(g) C. C(s) + ½O(g) CO(g) D. C(s) + O(g) CO(g) 2. When 1 mole of sodium bromide dissolves in water, the enthalpy change is -8 kJ mol¯¹. If the lattice energy of sodium bromide and the hydration energy of the Na⁺ ion are -736 kJ mol¯¹ and -406 kJ mol¯¹ respectively. What is the hydration energy of the Br¯ ion? A. -1150 kJ mol¯¹. B. -338 kJ mol¯¹. C. -322 kJ mol¯¹. D. +1150 kJ mol¯¹. 3. The standard reduction potentials, E° at 298 K for oxygen and manganese are as follows Electrode system E°/V O₂(g) ǀ H⁺(aq), H₂O₂(aq) ǀ Pt (s) +0.68 MnO₄¯(aq), H⁺(aq), Mn²⁺(aq) ǀPt(s) +1.52 Based on the above information, which of the following is true of a chemical cell which is constructed by combining the above two half-cells? A. H₂O₂ undergoes oxidation to O₂ B. H₂O₂ is a stronger oxidising agent than MnO₄¯ ion C. The platinum electrode for oxygen half-cell is the positive electrode. D. The e.m.f of the cell formed from the combination of the two-cells is +2.20 V. 4. A half-cell is formed by immersing a lead electrode in a saturated solution of lead(II) sulphate. The electrode potential of the half-cell is -0.36 V at 25°C. if the standard electrode potential of the Pb² ⁺/Pb halfcell is -0.13 V, what is the solubility product of lead(II) sulphate at 25°C? A. 1.6 x 10¯⁸ mol² dm¯⁶ B. 3.20 x 10¯⁸ mol² dm¯⁶ C. 2.56 x 10¯¹⁶ mol² dm¯⁶ D. 5.32 x 10¯²² mol ² dm¯⁶ 5. The following cell is set up to obtain pure copper by electrolysis as shown in the diagram below.
When a current of 40.00 A flows through the electrolyte for 26.8 minutes, the mass of anode decreases by 26.47 g. What is the percentage composition of copper in the copper-silver alloy? A. 50.0 % B. 60.0 % C. 70.0 % D. 80.0 % 1
6. The table below shows the reactivity of elements in Period 3 with oxygen. Na Very vigorous Mg Very vigorous Al Vigorous Si Slow reaction P Slow reaction S Slow reaction Cl No reaction Ar No reaction The trend of the elements across Period 3 shows that A. The elements become more electropositive B. The tendency of the elements to donate electrons decreases C. The reaction of the elements with oxygen becomes more exothermic D. The strength of the elements as an oxidizing agents decreases slowly 7. The properties of elements can be deduced from electronic configuration. Which statement is true about Na⁺ ion, Cl¯ ion, Ar atom and K⁺ ion? A. Na⁺ ion is bigger than Cl¯ ion B. The charge density of Na⁺ ion is lower than of Cl¯ ion C. The ionisation energy of K⁺ ion is higher than of Na⁺ ion D. Cl¯ ion, K⁺ ion and Ar atom have the same electronic configuration 8. The first ionisation energies of some elements in the Periodic Table are represented in the graph below.
Which statements about this graph are true? I elements S is in Group I of the Periodic Table II Atoms of elements Q and U contain two electrons in their valence shells III Atoms of element R contain half-filled p orbitals IV Element T is a non-conductor. A. I and II only B. I and IV only C. II and III only D. III and IV only 9. Which oxide will produce 1.0 mol dm¯³ aqueous solution with the lowest pH value? A. SO₂ B. MgO C. P₂O₅ D. Na₂O 10. Which of the following variation in properties is caused by the increase in the atomic or ionic size of the group 2 elements when going down the group? A. The decrease basicity of the oxides B. The increasing solubility of the sulphates C. The decreasing thermal stability of the carbonates D. The increasing reactivity of the elements towards water 2
11. Sulphur has a higher melting point than sodium because A. Sulphur is a metal but sodium is a metalloid B. The Van der Waals force in sulphur is stronger than the metallic bond in sodium C. The atomic radius of sulphur is larger than that of sodium is D. The presence of hydrogen bonding in sulphur 12. The diagram below shows part of the structure of a type of silicate
Which statement is true about this structure? A. The tetrahedral units form a planar structure B. Each silicon atom is bonded tetrahedrally to four oxygen atoms C. The structure is found in the mineral amphibole D. Each tetrahedral unit shares three oxygen atoms 13. X is an element in Group 17 of the Periodic Table. The percentage dissociation of hydrogen halide, HX at 2000°C is shown in the table below. HX HF HCl HBr HI Percentage 6x10¯⁵ 0.4 4 30 dissociation Which statement explains the thermal stability of HX on descending the group? A. The relative molecular mass increases B. The length of H-X bond increases C. The ionic characteristic of H-X bond decreases D. The intermolecular force increases 14. A thermally stable liquid, MCl₄ reacts with water to form a solution of low pH value. Which statement about M or its oxides is true? A. MO exists as simple molecules B. MO is an acidic oxide C. MO₂ is a reducing agent D. M is a good electrical conductor 15. Three d-block elements X, Y and Z (not the actual symbols for the elements) in the Periodic Table have the following properties. X: exhibits oxidation states of +1, +2, +3 and +4 only Y: Maximum oxidation state is +7 Z: Exhibits only one oxidation state of +2 Which statement is not true about X, Y and Z? A. X forms a compound with the molecular formula K₂XO₄ B. Y atom has seven valence electrons C. YO₄¯ is an oxidizing agents D. Z forms colourless ions
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Answer sheet for Section A (15 marks)
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Section B [15 marks] 4
Answer all questions in this section 16. The lattice energies of lithium chloride and sodium chloride are -848 kJ mol¯¹ and -776 kJ mol¯¹ respectively. (a) Define the term lattice energy by using lithium chloride as an example. [2 marks] ………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………… (b) State the relationship between lattice energy, enthalpy change of hydration and enthalpy change of solution ( ∆Hsol ) [1mark] ………………………………………………………………………………………………………………… ………………………………………………………………………………………………………………… (c) The values of the enthalpy changes of hydration for Li⁺ and Cl¯ are given in the following table. Ion Li⁺ Cl¯
Enthalpy change of hydration (kJ mol¯¹) -499 -381
(i) Calculate the enthalpy change of solution ( ∆Hsol ) of lithium chloride.
[2 marks]
(ii) Draw an energy level diagram to show the relationship between the energies involved in the dissolution of lithium chloride. [2 mark]
(iii) How would you expect the temperature to change when lithium chloride is dissolved in water? [1 mark] ………………………………………………………………………………………………………................
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17. (a) Cobalt is a transition element. It forms coloured complex ion. (i) Why is cobalt a transition element?
[1 mark]
……………………………………………………………………………………………………………….... (ii) Why does cobalt exhibit more than one oxidation state?
[1 mark]
……………………………………………………………………………………………………………… (b) A dilute aqueous solution of hexaaquacobalt(II) chloride, [Co(H₂O)₆]Cl₂ changes colour when exposed to heat. (i) State the colour change that occurs. [1mark] ………………………………………………………………………………………………………………… (ii) Draw the structural formula of the complex ion for [Co(H₂O)₆]Cl₂
[1 mark]
(iii) State the ligand of the complex ion
[1 mark]
………………………………………………………………………………………………………………… (iv) The hexaaquacobalt(II) ion loses two H₂O molecules when exposed to heat to form another octahedral complex ion. Draw the structural formula of this complex ion and state its name. [2 marks] Structural formula:
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Section C [30 marks] Answer two questions only in this section 18. Methanol, CH₃OH, is a potential sources of fuel. (a) An experiment was conducted to determine the enthalpy of combustion of methanol. 2.00 g of methanol was used to heat 150 g of water. The temperature of the water increased from 25°C to 87°C. (Given the specific heat capacity of water is 4.18 JK¯¹g¯¹) (i) Define the term standard enthalpy of combustion with reference to methanol [2 marks] (ii) Use the data above to determine the enthalpy of combustion of methanol [5 marks] (b) Methanol can be prepared by heating carbon monoxide with hydrogen at high pressure and in the presence of a catalyst according to the following equation. CO (g) + 2H₂ (g) CH₃OH Based on the following data, determine the enthalpy change of the above reaction. Enthalpy of formation of CO = -110.5 kJmol¯¹ Enthalpy of formation of CO₂ = -393.5 kJmol¯¹ Enthalpy of formation of H₂O = -285.8 kJmol¯¹ Enthalpy of formation of , CH₃OH = -726.3 kJmol¯¹
[8 marks]
19. (a) What do you understand by the term standard electrode potential? [2 marks] (b) By using data found in the Data Booklet, predict whether the following pairs of reagents are likely to react when mixed in acidified aqueous solution. Calculate the E° value and write a balanced equation for each reaction that may occur (i) I₂ (aq) and Cr³⁺(aq) (ii) H₂O₂(aq) and MnO₄¯(aq) [6 marks] (c) Plastic articles can be chromium plated by placing them in a bath of aqueous chromium (III) sulphate and electroplating. (i) What must be done to the plastic article before electroplating can be carried out? [2 marks] (ii) Draw a diagram of the electrical circuit for the electroplating cell. [2 marks] (d) If a current of 0.50 A was passed through the cell for 300 s, what would be the increase in mass due to the chromium plating? [3 marks] 20. (a) The standard enthalpy change of reactions for carbon and lead are as follows: C(g) + CO₂(g) 2CO(g) ∆H° = +172 kJ mol¯¹ Pb(s) + PbO₂(s) 2PbO(s) ∆H° = -159 kJ mol¯¹ Using the respective values of ∆H° for above reactions, explain the relative stability of the oxidation states of the elements in Group 14 of the Periodic Table. [4 marks] (b) (i) Draw the structure of carbon dioxide and silicon dioxide [2 marks] (ii) Although the bonding in carbon dioxide and silicon dioxide is covalent, carbon dioxide is a gas whereas silicon dioxide is a solid with high melting point. Explain this statement. [4 marks] (c) The boiling point of hydrogen halides are given in the following table:
(i) (ii)
Hydrogen halide HF HCl HBr HI Boiling point (K) 293 188 206 238 Sketch a graph to show the boiling points of the hydrogen halides [2 marks] Using the graph in (i), explain the variation in boiling points of the hydrogen halides. [3 marks]
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